Analysis of the effects of Faraday rotation on spaceborne polarimetric SAR observations at P-band

Spaceborne microwave observation of subcanopy and subsurface requires the polarimetric synthetic aperture radar (SAR) technology at lower microwave frequencies, such as P-band. However, SAR observation at P-band is remarkably influenced by the Faraday rotation (FR) effect through the ionosphere. An example in this paper illustrates why the measured polarimetric data with FR at P-band cannot be directly applied to terrain surface classification. We further present that the parameters u, nu, H, alpha, A for terrain surface classification derived from the polarimetric data without FR, which are recovered from the data with FR, can be applied to the surface classification there is a +/-pi/2 ambiguity error unresolved. Based on gradual change of the FR degree along a geographical location, a method to eliminate the +/-pi/2 ambiguity error is designed. Thus, the polarimetric scattering vector and Mueller matrix without FR and +/-pi/2 ambiguity can be fully inverted from the measured polarimetric data with FR.